Fix typo in the help message.

src/Docu.Console/Console/HelpMessage.cs

@@ -6,7 +6,7 @@ public class HelpMessage : IScreenMessage
     {
         public IEnumerable<string> GetBody()
         {
-            yield return "usuage: docu pattern.dll [pattern.dll ...] [pattern.xml ...]";
+            yield return "usage: docu pattern.dll [pattern.dll ...] [pattern.xml ...]";
             yield return "";
             yield return " * One or more dll matching patterns can be specified,";
             yield return "   e.g. MyProject*.dll or MyProject.dll";
@@ -19,4 +19,4 @@ public IEnumerable<string> GetBody()
             yield return "  --output=value  Sets the output path to value";
         }
     }
-}
+}